// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_FILES_IMPORTANT_FILE_WRITER_H_
#define BASE_FILES_IMPORTANT_FILE_WRITER_H_

#include <string>

#include "base/base_export.h"
#include "base/callback.h"
#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/strings/string_piece.h"
#include "base/threading/non_thread_safe.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
//#include "tencent/build/config_net.h"

namespace base {

class SequencedTaskRunner;
class Thread;

// Helper to ensure that a file won't be corrupted by the write (for example on
// application crash). Consider a naive way to save an important file F:
//
// 1. Open F for writing, truncating it.
// 2. Write new data to F.
//
// It's good when it works, but it gets very bad if step 2. doesn't complete.
// It can be caused by a crash, a computer hang, or a weird I/O error. And you
// end up with a broken file.
//
// To be safe, we don't start with writing directly to F. Instead, we write to
// to a temporary file. Only after that write is successful, we rename the
// temporary file to target filename.
//
// If you want to know more about this approach and ext3/ext4 fsync issues, see
// http://blog.valerieaurora.org/2009/04/16/dont-panic-fsync-ext34-and-your-data/
class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
public:
    // Used by ScheduleSave to lazily provide the data to be saved. Allows us
    // to also batch data serializations.
    class BASE_EXPORT DataSerializer {
    public:
        // Should put serialized string in |data| and return true on successful
        // serialization. Will be called on the same thread on which
        // ImportantFileWriter has been created.
        virtual bool SerializeData(std::string* data) = 0;

    protected:
        virtual ~DataSerializer() { }
    };

    // Save |data| to |path| in an atomic manner (see the class comment above).
    // Blocks and writes data on the current thread.
    static bool WriteFileAtomically(const FilePath& path, StringPiece data);

    // Initialize the writer.
    // |path| is the name of file to write.
    // |task_runner| is the SequencedTaskRunner instance where on which we will
    // execute file I/O operations.
    // All non-const methods, ctor and dtor must be called on the same thread.
    ImportantFileWriter(const FilePath& path,
        scoped_refptr<SequencedTaskRunner> task_runner);

    // Same as above, but with a custom commit interval.
    ImportantFileWriter(const FilePath& path,
        scoped_refptr<SequencedTaskRunner> task_runner,
        TimeDelta interval);

    // You have to ensure that there are no pending writes at the moment
    // of destruction.
    ~ImportantFileWriter();

    const FilePath& path() const { return path_; }

    // Returns true if there is a scheduled write pending which has not yet
    // been started.
    bool HasPendingWrite() const;

    // Save |data| to target filename. Does not block. If there is a pending write
    // scheduled by ScheduleWrite(), it is cancelled.
    void WriteNow(std::unique_ptr<std::string> data);

    // Schedule a save to target filename. Data will be serialized and saved
    // to disk after the commit interval. If another ScheduleWrite is issued
    // before that, only one serialization and write to disk will happen, and
    // the most recent |serializer| will be used. This operation does not block.
    // |serializer| should remain valid through the lifetime of
    // ImportantFileWriter.
    void ScheduleWrite(DataSerializer* serializer);

    // Serialize data pending to be saved and execute write on backend thread.
    void DoScheduledWrite();

    // Registers |on_next_successful_write| to be called once, on the next
    // successful write event. Only one callback can be set at once.
    void RegisterOnNextSuccessfulWriteCallback(
        const Closure& on_next_successful_write);

    TimeDelta commit_interval() const
    {
        return commit_interval_;
    }

#if 0 // ENABLE_TENCENT(DIRECT_PRECONNECT)
    void set_commit_interval(const TimeDelta& interval)
    {
        commit_interval_ = interval;
    }
#endif

private:
    // Helper method for WriteNow().
    bool PostWriteTask(const Callback<bool()>& task);

    // If |result| is true and |on_next_successful_write_| is set, invokes
    // |on_successful_write_| and then resets it; no-ops otherwise.
    void ForwardSuccessfulWrite(bool result);

    // Invoked once and then reset on the next successful write event.
    Closure on_next_successful_write_;

    // Path being written to.
    const FilePath path_;

    // TaskRunner for the thread on which file I/O can be done.
    const scoped_refptr<SequencedTaskRunner> task_runner_;

    // Timer used to schedule commit after ScheduleWrite.
    OneShotTimer timer_;

    // Serializer which will provide the data to be saved.
    DataSerializer* serializer_;

    // Time delta after which scheduled data will be written to disk.
#if 0 // ENABLE_TENCENT(DIRECT_PRECONNECT)
    TimeDelta commit_interval_;
#else
    const TimeDelta commit_interval_;
#endif

    WeakPtrFactory<ImportantFileWriter> weak_factory_;

    DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);
};

} // namespace base

#endif // BASE_FILES_IMPORTANT_FILE_WRITER_H_
